A content delivery network (CDN) service is a service for delivering content stably and rapidly. The CDN service delivers content to a user (client) at the request of the user using a plurality of content providing servers located in a network.
A description will be given of a conventional method for calculating a distance between a local DNS (LDNS) and a point of presence (POP) in the CDN with reference to FIG. 1.
A distance in a network may be a relative concept according to a data transfer rate between nodes which are devices constituting the network, rather than a physical or geographical distance between the nodes.
For example, when it is assumed that node 1 is a device located in Seoul, node 2 is a device located in New York and node 3 is a device located in Tokyo, a geographical distance between node 1 and node 3 is short. However, time required for communication between node 1 and node 2 may be shorter than time required for communication between node 1 and node 3 according to network state, for example, communication line type, performances or types of the corresponding devices. In this case, the distance between node 1 and node 2 can be regarded to be shorter than the distance between node 1 and node 3.
A distance in a network may be referred to as various terms such as RTT (Round Trip Time) and latency.
As shown in FIG. 1, in a CDN, a plurality of clients 100 is linked to an LDNS 110. Upon reception of a DNS resolution request from a client 100, the LDNS 110 delivers a reply to the DNS resolution request to a name server 120.
Here, an Internet protocol (IP) address transmitted by the name server 120 as a response is preferably linked to an optimal POP 130 in the CDN and a content server 140 (edge server or cache server) included in the POP 130.
To this end, the POP 130 includes a probe server 150 for calculating a network distance to the LDNS 110.
That is, the probe server 150 calculates the network distance between the POP 130 and the LDNS 110 using a ping test, trace route or the like and transmits the calculation result to the name server 120 or a load balancer (not shown) which can be separately present such that the name server 120 determines the optimal POP 130 and the content server 140 included in the corresponding POP on the basis of the calculation result.
Accordingly, in determination of the optimal content server 140 for providing content requested by the client 100 in the CDN, it is very important to calculate the distance between the LDNS 110 and the POP 130 in which content severs are present.
However, due to a complicated network configuration and for various reasons such as configurations of devices constituting a network, the probe server 150 may not perform a ping test or trace route for the LDNS 110.
In this case, the probe server 150 cannot calculate the distance between the POP 130 and the LDNS 110 and thus it is difficult to determine the optimal POP 130 or the optimal content server 140 in the CDN.